Re: A question about deleting a big file structure from a big disk in Jessie: Why does this work? I'm really worried.
Quoting Paul E Condon (pecondon@mesanetworks.net):
[...]
> Some time ago I decided to a make a copy of these data,
> so I would have more than one copy.
[...]
Is the copying between a USB disk and an internal, or between two
partitions on the same USB disk, or between two USB disks? (Ranked in
decreasing reliability in my own experience.)
> When I tried, the job would always crash well before completion.
What are the symptoms of a crash? (Hang, segfault, write-failure
as readonly, etc)
[...]
> But in both cases the
> deletion failed because 'gfx2' has been remounted read-only, which
> makes it impossible to update the target directory tree.
Do you watch /var/log/kern.log which this is going on. I find that
quite useful. For example, messages like
usb 1-8: reset high-speed USB device number 5 using ehci_hcd
are accompanied by a pause of anything up to a minute in file
transfer. I get these quite frequently if I do massive copies between
two USB disks, so I now stage such copies through the internal disk.
I'm not so unlucky as Bob appears to be (he says, touching wood), but
I do get occasional I/O errors on USB transfers, which can make the
disk readonly, but sometimes make it disappear altogether (ie it
gets unmounted, not remounted).
> I have not tried it, but from my investigation I'm sure that a
> massive delete of some obsolete file structure from the HD that
> was /dev/sda1 during Debian install would trigger a remount-ro,
> which surely would lead to a system crash in short order.
You get streams of error messages (like when the disk fills up)
but it shouldn't actually crash.
(OTOH when you get a kernel error, there can be circumstances where
the system will panic and *not* sync/write to the disk because to do
so could cause corruption.)
[...]
> I'm worried about what I found. I want to interest someone who has far
> more knowledge about how the kernel actually works internally to look
> into this. I done other experiments more complicated to report, I can't
> find anything comforting about this situation. If you think it's OK,
> you probably don't understand, IMHO.
My prejudices, based on no more than observations of my system, make me,
like Bob, suspect the interface rather than the kernel. My wife,
running windows, sees similar external symptoms (pauses, errors),
though neither of us would know how to observe them in like manner to
linux.
Just in passing, if clamav wakes up and spots the USB drive, file
transfers can stop for 10 or 15 minutes; the USB disk heads will still
be very active. I keep an xterm running top so I can spot that (and
other cpu-guzzlers like xulrunner).
Oh, and to David C, this happens irrespective of wheezy or jessie
(for me).
Cheers,
David.
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